A conventional rotation angle detection device includes a magnetic field generation section that rotates integrally with a rotating body, two yoke pieces that surround the magnetic field generation section, and two magnetic detection sections disposed between the two yoke pieces. The rotation angle detection device detects a rotation angle of the rotating body based on an output signal of the magnetic detection section which changes in accordance with a rotation of the rotating body. JP-A-2002-31505 discloses a rotation angle detection device in which a magnet as a magnetic field generation section is fixed in a groove of an end portion of a rotating shaft, and two Hall elements as magnetic detection sections are disposed in gaps between end portions of two yoke pieces formed by dividing a cylindrical member into halves.
Because the rotation angle detection device disclosed in JP-A-2002-31505 needs two yoke pieces and two Hall elements, the number of components is large and positional relationships among components are likely to vary. Thus, detection angles are likely to vary among individuals. Furthermore, because all the components are required regardless of a detection range, it is difficult to reduce a size of the rotation angle detection device.